1. Field of the Invention
The present invention relates to a high-density read-only optical disc on which large-capacity video and audio data are recorded and stored, and an optical disc apparatus and method of using the same.
2. Description of the Related Art
Recently, standardization of a new high-density rewritable optical disc, which can permanently record and store high-quality video data and audio data, e.g., a BD-RW (Blu-ray Disc Rewritable), is rapidly progressing. It is expected that related products will be developed, presented and commercialized in the near future.
With reference to FIG. 1, the structure of a BD-RW is divided into an inner surface, an intermediate surface and an outer surface. The inner surface includes a clamping area, a transition area, a BCA (Burst Cutting Area) and a lead-in area formed in that order. The intermediate and outer surfaces include a data area and a lead-out area, respectively.
The lead-in area is divided into a first guard-1 sub-area (“Guard 1”) , a Permanent Information and Control data sub-area (“PIC”), a second guard-2 sub-area (“Guard 2”), an “Info 2” sub-area, an Optimum Power Control sub-area (“OPC”), etc. The first guard-1 sub-area and the PIC sub-area are pre-recorded areas where data is previously recorded, whereas the lead-in area, the data area and the lead-out area are rewritable areas on which new data is rewritable.
The PIC sub-area is an area on which disc information is permanently recorded and stored. The disc information is basic information required for recording or reproducing user data on or from the data area. A HFM (High-Frequency Modulated) groove is formed on the PIC sub-area.
As shown in FIG. 2, the HFM groove has disc data modulated by a bi-phase modulation and stored thereon. For example, if the HFM groove is formed in the form of in-phase patterns in a recording section of 36T, a data value of “1” is recorded on the HFM groove. Further, if the HFM groove is formed in the form of anti-phase patterns in the recording section of 36T, a data value of “1” is recorded on the HFM groove.
A tracking servo for tracking a signal of the HFM groove, recorded on the PIC sub-area, uses the well-known push/pull method. In this case, an optical disc apparatus as shown in FIG. 3 includes a 2-element PD (photodiode) 12 for converting light received through an OL (Objective Lens) 10 and a CL (Collimating Lens) 11 into electric signals Ea and Eb; and a differential amplifier 13 for carrying out a differential amplification for the electric signals Ea and Eb outputted by the 2-element PD 12 and then outputting a tracking error signal TE=(Ea−Eb).
The optical disc apparatus performs a tracking servo operation by referring to the tracking error signal TE=(Ea−Eb). Moreover, in relation to a wobbled groove formed on the data area and the lead-in area, the optical disc apparatus enables a tracking servo operation for the wobbled groove to be carried out by referring to the tracking error signal TE=(Ea−Eb).
A BD-ROM (Blu-ray disc ROM (Read Only Memory)), in contrast with the above-described BD-RW, is a high-density read-only optical disc. As shown in FIG. 4, a structure of the BD-ROM is divided into an inner surface, an intermediate surface and an outer surface. The inner surface includes a clamping area and a lead-in area. The intermediate and outer surfaces include a data area and a lead-out area, respectively. The lead-in area has disc information recorded on the basis of an HFM (High-Frequency Modulated) groove as in the BD-RW. The data area and the lead-out area have data in pre-pit strings as in a conventional CD-ROM (Compact Disc-Read Only Memory) or DVD-ROM (Digital Versatile Disc-Read Only Memory).
If the lead-in area of the BD-ROM has the disc information recorded in the HFM groove as in the BD-RW, a tracking servo based on a push/pull method for the HFM groove is required. Simultaneously, another tracking servo based on a DPD (Differential Phase Detection) method for the pre-pit strings recorded on the data area and the lead-out area is also required.
Where only the HFM groove is formed on the lead-in area and the pre-pit data is not recorded on the lead-in area, there is a problem in that concatenated playback of the lead-in area and the data area is cut off because a PLL (Phase Locked Loop) circuit using an RF (Radio Frequency) does not operate.
FIG. 5 is a view illustrating the configuration of a tracking servo based on a DPD (Differential Phase Detection) method, which is applied to a conventional optical disc apparatus.
As shown in FIG. 5, the optical disc apparatus includes a 4-element PD (photodiode) 22 for converting light received through an OL (Objective Lens) 20 and a CL (Collimating Lens) 21 into electric signals Ea, Eb, Ec and Ed; phase detectors (PHs) 26, 27, 28 and 29 for detecting phases of the electric signals Eb, Ed, Ec and Ea; summing amplifiers 23 and 24 for summing the electric signals Eb and Ed outputted from the phase detectors 26 and 27 and the electric signals Ec and Ea outputted from the phase detectors 28 and 29 to generate summed electric signals Eb+Ed and Ec+Ea; and a differential amplifier 25 for carrying out a differential amplification for the summed electric signals Eb+Ed and Ea+Ec outputted by the summing amplifiers 23 and 24 and then outputting a tracking error signal TE=((Ea+Ec)−(Eb+Ed)).
Further, different tracking servo operations, i.e., a tracking servo operation based on a push/pull method and another tracking servo operation based on the DPD method, must be carried out for the same BD-ROM inserted into the optical disc apparatus. As a result, because the conventional optical disc apparatus requires a complex algorithm to control the different tracking servo operations, there is another problem in that a size of the conventional optical disc apparatus increases to accommodate these two tracking servo systems.